1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor.
2. Description of the Related Art
As semiconductor devices including semiconductors, logic circuits are given. Logic circuits include dynamic logic circuits and static logic circuits and are formed using transistors and the like. Dynamic logic circuits can store data for a certain period of time. Thus, leakage current from transistors causes more severe problems in dynamic logic circuits than in static logic circuits. Leakage current is attributed to off-state current flowing when transistors are turned off.
For example, in a dynamic circuit, leakage current is high when a MOS transistor which controls supply of electric charge to a dynamic node is off, which is regarded as a problem. To solve this problem, a structure has been suggested in which a MOS transistor circuit is inserted into a current path to a dynamic node (Patent Document 1).
Further, another structure is suggested in which a leakage current detecting circuit that detects current corresponding to leakage current and, in addition, a leakage current correcting circuit that operates in correcting leakage current are provided in a dynamic circuit (Patent Document 2).
Furthermore, added functions of logic circuits have been under consideration. For example, a reconfigurable logic circuit which can have a property of being dynamically reconfigurable (also referred to as a property of a dynamic reconfiguration) can be given. Suggested is a structure in which such a logic circuit includes a switching portion for switching between OR/AND and NOR/NAND/NOT (Patent Document 3).
The off-state current of a thin film transistor is 10−13 A to 10−14 A when Vgs is 0 V or lower (Patent Document 4).